When you exercise, your body needs extra energy because it’s working harder. This helps to:
- maintain your weight
- keep your bones strong
- maximise how well you train and perform
It's also important to make sure that you drink enough when you exercise. For more information on what's best to drink and how much, see Keeping hydrated for exercise.
We should all aim to eat a healthy balanced diet. But foods that contain carbohydrate are a key energy source for exercise, as it's broken down into glucose, which is your body’s main fuel.
You can store a small amount of glucose in your muscles as glycogen until you need it. So if you eat plenty of carbohydrates before you exercise, you can keep your supplies replenished. If you don’t have enough glycogen, you won’t have the energy to exercise to the best of your ability. You might also start to lose muscle mass. This is because your body may need to break down protein in your muscles to use as an alternative energy source.
The glycaemic index (GI) is a rating system for foods that contain carbohydrates. It shows how quickly each food affects the sugar levels in your blood.
Click on the image to open the glycaemic index.
As a general guide, your daily intake of energy should be around:
- 2,500 calories for men
- 2,000 calories for women
You might see these values listed on food labels. The figures are based on average weights and physical activity levels so your personal energy needs can vary from these.
There are ways to be more precise and calculate what you personally need to keep you going. One way is by working out your basal metabolic rate (BMR). This is the number of calories you need to keep your body functioning properly when you’re resting. Here's how to work out your BMR in kcal per 24hours.
BMR for men = 66.47 + (13.7 multiplied by your weight in kg) + (5 multiplied by your height in cm) − (6.8 multiplied by your age in years)
BMR for women = 655.1 + (9.6 multiplied by your weight in kg) + (1.8 multiplied by your height in cm) − (4.7 multiplied by your age in years)
How much activity you do Calories you need = Little/no exercise BMR multiplied by 1.2 Light exercise BMR multiplied by 1.375 Moderate exercise (three to five days a week) BMR multiplied by 1.55 Very active (six to seven days a week) BMR multiplied by 1.725 Extra active (very active and physical job) BMR multiplied by 1.9
As you can see, the calories you consume each day will depend on how much you exercise you do. It also depends on what you’re aiming to achieve – for example, if you're trying to lose weight. You may also need to take into account other factors, such as how long you work out for and the environment in which you exercise.
This can all get quite complex so it might be worth getting advice from a dietitian if you feel you need to. Together you can work out a healthy eating diet plan that suits your needs and goals.
What you eat before exercising will determine how much energy you have and how well you perform. Three to four hours before you exercise, eat a meal that contains:
- plenty of carbohydrate – this will increase both your blood glucose and your glycogen levels
- a moderate amount of protein – this will help your body to recover after exercise
- only a low amount of fat and fibre – this can take a long time to digest and may give you stomach problems
If you’re going to be doing some particularly strenuous exercise, have a small healthy snack an hour beforehand. And if you're hitting the gym straight after work and don’t have much time to eat, have something lighter that also contains plenty of carbohydrate. Have some juice, fruit, or crackers. They're easier to digest and will provide energy more quickly.
You might need to experiment with the timings of your meal and/or snack to make sure that you don’t feel uncomfortable once you start exercising.
Here are some ideas for snacks and meals to have before you exercise.
- Chicken sandwich
- Pasta with tomato-based sauce and vegetables
- Baked beans on toast
- Porridge made with skimmed or semi-skimmed milk
- Fruit (such as a banana)
- Smoothie made with skimmed or semi-skimmed milk
- Cereal or energy bar
- Small carton of fruit yogurt
If you’re planning on doing some serious exercise, such as a marathon, it’s a good idea to follow a carbohydrate-loading programme.
This involves first exercising to a point where you feel like you've used up your energy in your muscles. This workout should be identical (or close to) your upcoming event to make sure you run down the energy stores from the right muscles. You then follow this by reducing your training and increasing how much carbohydrate you eat in the final three days before your event. Aim to eat 9 to 10g of carbohydrate per kg of body weight.
If you eat while you're exercising, it will help to provide glucose to your working muscles. This will stop you from getting tired too quickly and critically, increase your endurance and performance. How much you need to eat (and if you do at all) will depend on how long you’re active for.
If you’re exercising continuously for more than an hour, aim to eat 30 to 60g of carbohydrate every hour. You can either get this from a sports drink or carbohydrate-rich food that's easy to digest, such as a cereal bar. Eat this in small amounts at intervals, rather than the whole lot all in one go.
Here are some ideas for snacks during exercise.
Portion size that provides 50g carbohydrate
Bananas Two (medium-sized) Dried apricots 15 Cereal bar Three 25g bars – but check the label
It’s really important to eat something soon after you exercise to replenish your stores of glycogen. How much and when you eat will depend on how long and how hard you've been exercising, and when you plan to exercise next.
In general, aim to eat within the first half an hour after you finish an exercise session. Eat about 1.5g of carbohydrate per kg of your body weight. For example, if you weigh 60kg, you'll need to eat about 90g of carbohydrate. If you don't feel like eating, have a high-carbohydrate drink instead. Include a good portion of starchy foods such as bread, pasta, rice or potatoes in your next meal too. And include some protein in your meal because it can help to build and repair your muscle tissue.
Here are some ideas for snacks after you've been exercising.
- Malt loaf
- One sports bar (that contains carbohydrate and protein)
- A handful of dried fruit
- Fruit and yoghurt smoothie
- Low fat chocolate milk
- British Nutrition Foundation
020 7404 6504
- Sport. British Dietetic Association. www.bda.uk.com, accessed reviewed April 2014
- Dietary reference values for energy. Scientific Advisory Committee on Nutrition. www.gov.uk, accessed 11 November 2011
- Zoorob R, Parrish M, O'hara H et al. Sports nutrition needs: before, during, and after exercise. Prim Care 2013; 40(2):475–86. doi: 10.1016/j.pop.2013.02.013
- Carbohydrates. British Dietetic Association. www.bda.uk.com, accessed reviewed April 2013
- Nutrition for athletes. The Nutrition Working Group of the International Olympic Committee. www.olympic.org, accessed April 2012
- Sports nutrition. American Academy of Orthopaedic Surgeons. www.orthoinfo.aaos.org, accessed December 2014
- Macronutrients and energy balance. Oxford handbook of nutrition and dietetics (online). Oxford Medicine Online. www.oxfordmedicine.com, January 2012 (online version)
- Draft carbohydrates and health report. Scientific Advisory Committee on Nutrition. www.gov.uk, accessed 2014
- BMR calculator. Diabetes.co.uk. www.diabetes.co.uk, accessed September 2015
- Selecting and effectively using sports drinks, carbohydrate gels and energy bars. American College of Sports Medicine. www.acsm.org, accessed 2011
- Eating for sport and exercise. British Nutrition Foundation. www.nutrition.org.uk, accessed January 2012
- British Nutrition Foundation
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